Protective effect of the bile salt hydrolase-active Lactobacillus reuteri against bile salt cytotoxicity

Bacterial bile salt hydrolysis is considered a risk factor for the developm ent of colon cancer because of the risk of forming harmful secondary bile s alts after an initial deconjugation step. In this study, the influence of e nhanced bacterial bile salt transformation by the bile salt hydrolase-activ e Lactobacillus reuteri was studied in batch culture using the microbial su spension of the Simulator of the Human Intestinal Microbial Ecosystem; (SHI ME), which was supplemented with oxgall at 5 g/l or 30 g/l. Changes in the fermentative capacity of the microbial ecosystem and the (geno)toxic proper ties of the SHIME supernatants were investigated. Increasing concentrations of oxgall inhibited the fermentation. Transient cell toxicity was observed for samples supplemented with 5 g oxgall/l, while samples with 30 g oxgall /l exhibited toxicity. The results of the haemolysis test suggest that the detrimental effects were probably due to the membrane-damaging effects of b ile salts. In all cases, the adverse effects could be counteracted by the a ddition of 7.5 +/- 0.5 log(10) CFU L. reuteri/ml. Plausible mechanisms for the protective properties of L. reuteri could involve a precipitation of th e deconjugated bile salts and a physical binding of bile salts by the bacte rium, thereby making the harmful bile salts less bioavailable.